Circuit for multiplying an analog value by a digital value

ABSTRACT

A multiplication circuit directly multiplying an analog and a digital data without converting analog/digital or digital/analog converting. An analog input voltage is controlled by a switching signal of a digital voltage so as to generate an analog output or cut-off the outputs. Digital input signals b 0  to b 7  of a plural number of bits is integrated giving weights by means of a capacitive coupling, and a sign bit is added by a capacitive coupling CP with a double weight of the most significant bit (&#34;MSB&#34;) of the digital input.

FIELD OF THE INVENTION

The present invention relates to a multiplication circuit.

BACKGROUND OF THE INVENTION

In recent years, there are arguments about a limitation of a digital computer because of expotential increase in the amount of money for investments for equipment concerning to a minute processing technology. Here, an analog computer is calling attention. On the other hand, stored conventional digital technology should be used and both workings of a digital and an analog processings are necessary, and operational processing system including an analog data and a digital data is important.

However, conventionally, such an operational circuit including both an analog and a digital data without analog/digital or digital/analog converting is not known.

SUMMARY OF THE INVENTION

The present invention is invented so as to solve the conventional problems and has a purpose to provide a multiplication circuit capable of directly multiplying an analog data and a digital data without analog/digital or digital/analog converting.

A multiplication circuit according to the present invention controls an analog input voltage by a switching signal of a digital voltage so as to generate an analog output or cut-off the output. A digital input signal of a plural number of bits with giving weights by means of a capacitive coupling, and a sign bit is added by a capacitive coupling with a double of the MSB of the digital input.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit showing the first embodiment of a multiplication circuit according to the present invention.

FIG. 2 is a detailed diagram showing inverter circuits INV₁ and INV₂.

FIG. 3 is an inverter circuit in FIG. 2.

FIG. 4 is a circuit detailedly showing switching circuits from SW₁ to SW₈.

FIG. 5 is a circuit diagram showing the inside of a switching circuit SW₉.

PREFERRED EMBODIMENT OF THE INVENTION

Hereinafter, an embodiment of a multiplication circuit according to the present invention is described with referring to the attached drawings.

In FIG. 1, a multiplication circuit M has a plural number of switching circuits from SW₁ to SW₈ connected with an analog input voltage X and digital input voltages from b₀ to b₇ corresponding to each bit of a digital data as a control signal to these switching circuits. Outputs of switching circuits are connected with each capacitor in a capacitive coupling CP parallelly connecting a plural number of capacitors from CC₀ to CC₇, and an output of CP generates an output as shown by following formula.

    V.sub.3 ==V.sub.2 (C.sub.3 /C.sub.2)=X (C.sub.3 /C.sub.2)  (11)

This formula is rewritten as follows under a condition of C₂ =C₃.

    Y=X                                                        (12)

As mentioned above, products of an analog input voltage X and a digital input voltage (from b₀ to b₇) are directly calculated in a multiplication circuit M and it is possible to perform inverted processing corresponding to sign bit s at INV₁.

Outputs of INV₁ and INV₂ are connected with a switching circuit SW₉, and SW₉ is switched by a sign bit s of a digital data. The switch SW₉ outputs V₂ or V₃ alternatively, as an output voltage Y. An inverted output V₂ of Y is output when a sign bit s is equal to 1 (high level), and a non-inverted output V₂ is output when a sign bit s is equal to 0 (low level).

FIG. 2 shows the inside of composition of inverter circuits INV₁ and INV₂, and FIG. 3 shows an inverter circuit in FIG. 2.

As FIG. 2 shows, by serially connecting a plural number of inverters from I₁ and I₃, an output accuracy becomes higher. Inverters from I₁ to I₃ consist of nMOS and pMOS the drains of pMOS is connected with a positive voltage, the source of pMOS is connected with the drain of nMOS, and the source of nMOS is connected with a negative voltage. An input voltage is input to the gates of nMOS and pMOS. An output is generated from the junctive of both MOSs.

FIG. 4 shows the switching circuits from SW₁ to SW₈ in detail. The switching circuit is a CMOS switch consisting of a CMOS Tr₁ and a dummy transistor Tr₂. An output voltage X is input to a drain of Tr₁, and an output is generated at the junctive of Tr₁ and Tr₂. A digital input voltage is invertedly connected to the gate of pMOS of Tr₁ and the gate of nMOS of Tr₂ and non-invertedly connected to the gate of mMOS of Tr₁ and the gate of pMOS of Tr₂. As a result, it is possible to realize opening and closing of an analog input voltage with little voltage drop at a switch.

FIG. 5 shows the switching circuit in detail. V₂ and V₃ are connected with a pMOS source side in two CMOSs Tr₃ and Tr₄, and pMOS drain side is connected with a common capacitance C₄. Sign bit s is directly input to a nMOS gate of Tr₃ and pMOS gate of Tr₄, and an signal inverted by an inverter I₄ is input to a gate of pMOS of Tr₃ and a gate of nMOS of Tr₄. When a sign bit s is equal to 1, then Tr₃ becomes conductive and an inverted output V₂ is impressed to C₄. When a sign bit s is equal to 0, then Tr₄ is conductive so that non-inverted output V₃ is impressed to C₄. Therefore, it is possible to generate positive and negative output corresponding to a sign bit.

As mentioned above, a multiplication circuit according to the present invention controls an analog input voltage by a switching signal of a digital voltage so as to generate an analog output or cut-off the outputs. A digital input signal of a plural number of bits is integrated giving weights by means of a capacitive coupling, and a sign bit is added by a capacitive coupling with a double weight of the MSB of the digital input so that it is possible to provide a multiplication circuit directly multiplying an analog and a digital data without converting analog/digital or digital/analog converting. 

What is claimed is:
 1. A multiplication circuit comprising:i) a capacitive coupling element which comprises a plurality of first capacitors connected in parallel with capacitive values corresponding to weights of each bit of a digital data; ii) a first switching circuit connected with the first capacitors of said capacitive coupling element, said switching circuit being opened and closed by a digital voltage corresponding to each bit of said digital data; iii) a first inverter connected with an output of said capacitive coupling element; iv) a second capacitor connected with an output of said first inverter; v) a second inverter connected with said first inverter through said second capacitor; vi) a second switching circuit connected with an output of the second inverter and said output of said first inverter for outputting alternatively one of said outputs; and vii) an analog input voltage connected with said first switching circuit.
 2. A multiplication circuit as claimed in claim 1, wherein said first and the second switching circuits comprises CMOS.
 3. A multiplication circuit as claimed in claim 1, wherein said first and second switching circuit comprises CMOS and a dummy transistor.
 4. A multiplication circuit as claimed in claim 1, wherein said first inverter feeds back an output to an input through a capacitor with a capacitance equal to a total capacitance of a capacitive coupling.
 5. A multiplication circuit as claimed in claim 1, wherein said second inverter is connected at said output with an input of said second inverter through a capacitor with capacity equal to a capacitance of said second capacitor, whereby said output is fed back to said input.
 6. A digital/analog multiplier, comprising:a bridge of switching elements, each receiving an analog signal to be multiplied, and each receiving a respective bit of a digital signal to be multiplied, said bridge of switching elements selectively switching on or off voltages dependent on bit of said digital signal and producing an output signal indicative of a multiplication product between said analog signal and said digital signal; an inverting element, receiving the output of said bridge, and inverting a sense of an analog voltage represented thereby; and a switch, receiving a sign bit of the digital signal, and receiving an inverted an a non-inverted result of multiplication, said sign bit selecting which of said inverted or non-inverted output is produced.
 7. A system as in claim 6 wherein said bridge includes a plurality of capacitors which sum together outputs of said switches.
 8. A system as in claim 7 wherein said switches receive said digital bits to turn said switches on and off.
 9. A system as in claim 7 wherein said capacitors have values which respectively weight various parts of the bridge.
 10. A multiplier as in claim 6 wherein said inverting element includes at least three inverters in series.
 11. A multiplier as in claim 10 wherein at least one of said inverters is of an nMOS type and at least another of said inverters is of a pMOS type. 